1. Field of the Invention
The invention generally relates to the field of immunology and immunotherapy, and more specifically to the treatment of autoimmune and inflammatory diseases by competitive inhibitors of tumor necrosis factor alpha.
2. Summary of the Related Art
Inflammation is a complex biological response of the body's tissues to pro-inflammatory agents, such as pathogens. In this response, the body attempts to remove the pro-inflammatory agent while initiating a healing process. In certain diseases that have an inflammatory component (e.g., autoimmune diseases), the body's immune systems respond inappropriately to a non-foreign substance. In this situation, the immune system causes damage to the body's own tissues.
Historically, autoimmune and inflammatory disease have been treated with non-steroidal anti-inflammatory drugs (NSAIDs—such as aspirin, ibuprofen or naproxen), corticosteroids (such as prednisone), anti-malarial medications (such as hydroxychloroquine), or other non-specific medications, including methotrexate, sulfasalazine, leflunomide, cyclophosphamide, and mycophenolate. However, the effectiveness of these treatments is limited.
More recently, competitive inhibitors of tumor necrosis factor alpha (TNF-α) have been developed as more specific treatments for autoimmune and inflammatory disorders. Such competitive inhibitors include etanercept (Embrel®), infliximab (Remicade®), and adalimubab (Humira®). These agents act by binding to TNF-α, thereby making it unavailable to its receptor and preventing it from initiating an inflammatory cascade, and represent a substantial improvement in the treatment of autoimmune and inflammatory disorders.
Such competitive inhibitors of TNF-α have been approved for the treatment of a wide variety of such diseases, including rheumatoid arthritis, arthritis of psoriasis, psoriasis, uveitis, ankylosing spondylitis, Crohn's disease, and sarcoidosis.
Competitive inhibitors of TNF-α have been shown to be useful in other applications as well. Popivanova et al. (2008) J. Clin. Invest. 118:560-70, teaches that blocking of TNF-α in mice reduces colorectal carcinogenesis associated with chronic colitis. Fries et al. (2008) Int. J. Med. Sci. 5: 169-80, and (2008) Am. J. Physiol. Gastrointest. Liver Physiol. 294:G938-G947, respectively, teach that infliximab and etanercept reduce enterocyte apoptosis in experimental colitis in mice and prevented loss of occludin and zonula occludens-1 in enterocyte tight junctions. Coppieters et al. (2006) Arthritis & Rheumatism 54:1856-66, teaches that the camelid anti-TNF VHH protein exceeds that of infliximab and adalimumab in a mouse model of rheumatoid arthritis. Zalevsky et al. (2007) J. Immunol. 179:1872-83, teaches that dominant-negative inhibitors of TNF attenuate experimental arthritis in a mouse model. Rubbert-Roth and Finckh (2009) Arthritis Res. Ther. 11(Suppl 1):S1, reviews the limitations of effectiveness of the FDA approved competitive inhibitors of TNF-α.
In an alternative approach, Newton et al. (2001) Ann. Rheum. Dis. 60:iii25-iii32, teaches that inhibitors of TACE, the enzyme that converts pro TNF-α to TNF-α are effective in a mouse model of arthritis.
Unfortunately, all of the currently approved competitive inhibitors of TNF-α have been implicated in the development of severe infections, including tuberculosis, sepsis, and fungal infections. Decreased white and red blood cell and platelet counts and increased incidents of certain cancers have also been associated with treatment with these drugs.
Toll-like receptors (TLRs) are present on many cells of the immune system and have been shown to be involved in the innate immune response (Hornung et al., (2002) J. Immunol. 168: 4531-37). In vertebrates, this family consists of ten proteins called TLR1 to TLR10, which are known to recognize pathogen associated molecular patterns from bacteria, fungi, parasites, and viruses (Poltorak et al. (1998) Science 282:2085-88; Underhill et al. (1999) Nature 401:811-15; Hayashi et al. (2001) Nature 410:1099-103; Zhang et al. (2004) Science 303:1522-26; Meier et al. (2003) Cell. Microbiol. 5:561-70; Campos et al. (2001) J. Immunol. 167:416-23; Hoebe et al. (2003) Nature 424:743-48; Lund (2003) J. Exp. Med. 198:513-20; Heil et al. (2004) Science 303:1526-29; Diebold et al. (2004) Science 303:1529-31; Hornung et al. (2004) J. Immunol. 173:5935-43). TLRs are a key means by which mammals recognize and mount an immune response to foreign molecules and also provide a means by which the innate and adaptive immune responses are linked (Akira et al. (2001) Nat. Immunol. 2:675-80; Medzhitov (2001) Nature Rev. Immunol. 1:135-45). TLRs have also been shown to play a role in the pathogenesis of many diseases, including autoimmunity, infectious disease, and inflammation (Cook et al. (2004) Nat. Immunol. 5:975-79) and the regulation of TLR-mediated activation using appropriate agents may provide a means for disease intervention.
Some TLRs are located on the cell surface to detect and initiate a response to extracellular pathogens and other TLRs are located inside the cell to detect and initiate a response to intracellular pathogens. Table 1 provides a representation of TLRs, the cell types containing the receptor, and the known agonists thereof (Diebold et al. (2004) Science 303:1529-31; Liew et al. (2005) Nature 5:446-58; Hemmi et al. (2002) Nat. Immunol. 3:196-200; Jurk et al. (2002) Nat. Immunol. 3:499; Lee et al. (2003) Proc. Natl. Acad. Sci. U.S.A. 100:6646-51); (Alexopoulou (2001) Nature 413:732-38).
TABLE 1Cell TypesTLR MoleculeAgonistContaining ReceptorCell Surface TLRs:TLR2bacterial lipopeptidesMonocytes/macrophages;Myeloid dendritic cells;Mast cellsTLR4gram negative Monocytes/macrophages;bacteriaMyeloid dendritic cells;Mast cells;Intestinal epitheliumTLR5motile bacteriaMonocyte/macrophages;Dendritic cells;Intestinal epitheliumTLR6gram positiveMonocytes/macrophages;bacteriaMast cells;B lymphocytesEndosomal TLRs:TLR3double strandedDendritic cells;RNA virusesB lymphocytesTLR7single strandedMonocytes/macrophages;RNA viruses;Plasmacytoid dendriticRNA-immunoglobulincells; B lymphocytescomplexesTLR8single strandedMonocytes/macrophages;RNA viruses;Dendritic cells; Mast cellsRNA-immunoglobulincomplexesTLR9DNA containingMonocytes/macrophages;unmethylatedPlasmacytoid dendritic“CpG” motifs; DNA-cells; B lymphocytesimmunoglobulincomplexes
Certain unmethylated CpG motifs present in bacterial and synthetic DNA have been shown to activate the immune system and induce antitumor activity. (Tokunaga et al. (1984) J. Natl. Cancer Inst. 72:955-62; Shimada et al. (1986) Jpn. J. Cancer Res. 77:808-16; Yamamoto et al. (1986) Jpn. J. Cancer Res. 79:866-73). Other studies have shown that antisense oligonucleotides containing CpG dinucleotides also stimulate immune responses (Zhao et al. (1996) Biochem. Pharmacot. 26:173-82). Subsequent studies demonstrated that TLR9 recognizes unmethylated CpG motifs present in bacterial and synthetic DNA (Hemmi et al. (2000) Nature 408:740-45). Other modifications of CpG-containing phosphorothioate oligonucleotides can also affect their ability to act as modulators of immune response through TLR9 (see, e.g., Zhao et al. (1996) Biochem. Pharmacol. 51:173-82; Zhao et al. (1996) Biochem Pharmacol. 52:1537-44; Zhao et al. (1997) Antisense Nucleic Acid Drug Dev. 7:495-502; Zhao et al. (1999) Bioorg. Med. Chem. Lett. 9:3453-58; Zhao et al. (2000) Bioorg. Med. Chem. Lett. 10:1051-54; Yu et al. (2000) Bioorg. Med. Chem. Lett. 10:2585-88; Yu et al. (2001) Bioorg. Med. Chem. Lett. 11:2263-67; and Kandimalla et al. (2001) Bioorg. Med. Chem. 9:807-13). In addition, structure activity relationship studies have allowed identification of synthetic motifs and novel DNA-based compounds that induce specific immune response profiles that are distinct from those resulting from unmethylated CpG dinucleotides. (Kandimalla et al. (2005) Proc. Natl. Acad. Sci. U.S.A. 102:6925-30; Kandimalla et al. (2003) Proc. Nat. Acad. Sci. U.S.A. 100:14303-08; Cong et al. (2003) Biochem Biophys Res. Commun. 310:1133-39; Kandimalla et al. (2003) Biochem. Biophys. Res. Commun. 306:948-53; Kandimalla et al. (2003) Nucleic Acids Res. 31:2393-400; Yu et al. (2003) Bioorg. Med. Chem. 11:459-64; Bhagat et al. (2003) Biochem. Biophys. Res. Commun. 300:853-61; Yu et al. (2002) Nucleic Acids Res. 30:4460-69; Yu et al. (2002) J. Med. Chem. 45:4540-48; Yu et al. (2002) Biochem. Biophys. Res. Commun. 297:83-90; Kandimalla et al. (2002) Bioconjug. Chem. 13:966-74; Yu et al. (2002) Nucleic Acids Res. 30:1613-19; Yu et al. (2001) Bioorg. Med. Chem. 9:2803-08; Yu et al. (2001) Bioorg. Med. Chem. Lett. 11:2263-67; Kandimalla et al. (2001) Bioorg. Med. Chem. 9:807-13; Yu et al. (2000) Bioorg. Med. Chem. Lett. 10:2585-88; Putta et al. (2006) Nucleic Acids Res. 34:3231-38).
The selective localization of TLRs and the signaling generated therefrom provides some insight into their role in the immune response. The immune response involves both an innate and an adaptive response based upon the subset of cells involved in the response. For example, the T helper (Th) cells involved in classical cell-mediated functions such as delayed-type hypersensitivity and activation of cytotoxic T lymphocytes (CTLs) are Th1 cells. This response is the body's innate response to antigen (e.g., viral infections, intracellular pathogens, and tumor cells), and results in a secretion of IFN-gamma and a concomitant activation of CTLs. Alternatively, the Th cells involved as helper cells for B-cell activation are Th2 cells. Th2 cells have been shown to be activated in response to bacteria and parasites and may mediate the body's adaptive immune response (e.g., IgE production and eosinophil activation) through the secretion of IL-4 and IL-5. The type of immune response is influenced by the cytokines produced in response to antigen exposure and the differences in the cytokines secreted by Th1 and Th2 cells may be the result of the different biological functions of these two subsets.
As a result of their involvement in regulating an inflammatory response, TLRs have been shown to play a role in the pathogenesis of many diseases, including autoimmunity, infectious disease, and inflammation (Papadimitraki et al. (2007) J. Autoimmun. 29: 310-18; Sun et al. (2007) Inflamm. Allergy Drug Targets 6:223-35; Diebold (2008) Adv. Drug Deliv. Rev. 60:813-23; Cook et al. (2004) Nat. Immunol. 5:975-79; Tse and Horner (2008) Semin. Immunopathol. 30:53-62; Tobias and Curtiss (2008) Semin. Immunopathol. 30:23-27; Ropert et al. (2008) Semin. Immunopathol. 30:41-51; Lee et al. (2008) Semin. Immunopathol. 30:3-9; Gao et al. (2008) Semin. Immunopathol. 30:29-40; Vijay-Kumar et al. (2008) Semin. Immunopathol. 30:11-21).
While activation of TLRs is involved in mounting an immune response, an uncontrolled stimulation of the immune system through TLRs may exacerbate certain diseases in immune compromised subjects. Such uncontrolled stimulation may also contribute to autoimmunity or inflammatory disorders.
Thus, there is a need for improved approaches to the treatment of autoimmune and inflammatory diseases.